Radio receiving system



Oct. 9, 1951 M. G. cRosBY RADIO RECEIVING SYSTEM` Oct. 9, 1951 M.`G.CROSBY RADIO RECEIVING SYSTEM 5 Sheets-Sheet 2 Filed Feb. l, 1945INVENTOR. /z/,P/PAY (kayak 5 Sheets-Sheet 3 Filed Feb. l, 1945 INVENTORMPP/(Y 6, OPMBY Oct. 9, 1951 M. G. CROSBY 2,570,431

' RADIO RECEIVING SYSTEM Filed Feb. 1, 1945 5 sheets-sheet 4 INVENTOR.mamy/6, (fasx BY /w-MM/ ATTO/Enfin 0t- 9 1951 M, G. CROSBY f RADIORECEIVING SYSTEM 5 Sheets-Sheet 5 Filed Feb. l, 1945 MII. @www PatentedOct. 9, 1951 VMurray G. .Cr0sby,.Riverhead,.N. QY., assignor toRadio'Corporationof America, a. corporationf DelawareApplication-February 1, 1945,# Serial No.i57:5;658

14.Claims. .l :This invention fis van improvedgdiversity ,fre-.fceivin'g system .,for.:.over.coming the effectsfof :fading:

:In: my copendin'gapplication SerialNo./483,989,

filed April 22, 1943, now U. S. Patent v2,4 .O;868,

there iis describeda .diversity'receiving system in whichethe strongestsignal; of the receiverlchan- A-nelsais:rapidlyraselected.; for `:.use.:in .the vcommon output .circuiti inl order-to prevent,;the:possibility`offgmore thanpnereceiver channel contributing fto: thexQmmOn-output. atone time. and thus producedistortion :In-theasystem of my copending'ffapplication, .supra, l.each channel has a vrectifier :therein andftherectified currentsrfrom.all chan- .:nelsiappeargas a potentialdrop'across a common* 1- rresistor. -The .'ow yof rectified vcurrent jin :the fcoinmon: resistortdue .to ,thegstrongest` signal producesazbiastosreducethe responsiveness of -the '..zch'annels carrying the weaker,signals.

lThe present-invention,provides a diversity re-f:

ceivingsystem ofV improved. sensitivity by -reducing `the :amount ofoutput: from each receiverto :loeI controlled. In accordance withoneaspect of vzthe invention, Iobtain an audioV frequency outputdirectly from'the receiver `under control of recti- `fied intermediatefrequency signal energy. -In a this way-I am able to :separate thedirectfcurrent u controlling bias :from :the output .voltages ".tol becombined. This feature of the'presentzinvention .enables az-reduction inthe'level fof the voltagesiq'` tobe combined, asasresult of whichthereis an improvementein the sensitivity ofthe selecting action. Inaccordance with another :aspect of :the invention,` I separate theintermediate: fre- .quency .signal current. from the directa current :it

" bias, .and pass .them over :separate f paths before.fsuperimposingthem on ronefanother. I am-thus able. to superimposeythe. intermediate frequency .current on the direct current at 'afreduced llevel :of intermediate "frequency current. is i thus achievedbetween lthe alternatingwcurrent -signal voltages `to "be lcombine'd andthe controlling -or rectified direct-current controlling voltage.This-separation'fisfaccomplished @with simplicity andV amin-imum ofcircuit elements.

Af-*more'fdetailed descriptionof the invention l"follows inconjunction-f-With vdrawings, wherein:

"Figs, `1 to 5, inclusive,--illustratey five-different diversityreceiving rsystem embodiments =of fthe invention.

-Inthe Asystem-ofFig. '1, the audiov frequency outputs from the'different channels `are-com- Ibined and are under control of'theintermediate lfrequency rectified signal.

4In-the system ofFFig, 2, the intermediate fre- Separationy..quencyoutputs from the different channels .are icombinedundericontrol of ithev intermediate .fre- -.q1.1ency rectified, signal.

,-sIig.` 3 illustrates a modification of .the system off-Fig.;2, .usefulfor receiving yphase or frequency -modulatedsignals especially desirablefor -pre- `venting -cancellation of `theoutputs of there- .ceiversnormally brought .about by equal Y signals -.of oppositephase inftwoxormore channels.y

The system of Fig. .4 f is somewhat similar .to that of Fig. 2, exceptthat use is made inFig. 4

:of the so-.calledinnite impedance'diode .(three- .element vacuumtube)Fig. 5 .is La `modification vofF-iglutilizingqdiffferential..diodeiresstors in'circuit -with .the outputs.of vthe frequency;` modulation receivers.

Throughout thegures of the drawings, the

vsame parts fare-.represented by the same .refer- .ence characters.

:The .system Y of Y Fig.` 1 .shows.-.three ysimilar -receivers.designatedChannel #1, Channel #2,

:and ifChannel .4t-3. -Since'the apparatus at the .three receivers raresimilar, and similarly arranged,fthef.units--,of. thesecond-and thirdVreceivers. have `rbeen. given-tl-iewsamer reference numerals :as-.theLfirst receiverywith the V.additionof prime :designationsl.The-.operation o f all three'receiv- :.ers;is:.-,theesame. ;Eachreceiver includes-an anvrtenna'A, A or; AZga. radio frequency amplifierB or-'-B,,a frequency'converterC, Cor C'., andan intermediatefrequencygamplier D, D'Ior D". `Eachfreceiver may 'have its ovvn localbeatying 4oscillatorlnot shown) connected to thefre- .quency converteror, if desired, there may be ...used-ia common beatingoscillatorfor allthree .receivers :Theoutput rcircuits of the intermediate.-frequencyamplifiers feed Y into receivers -.R,

.,R; and fR". :These receivers maybe frequency modulation or:phasemodulaticn apparatus with f orfwithoutpa,v limiter, or `.anamplitude modulation `typercf receiver, asdeSignated-` inthe drawing'.

Thegoutputs-from the receivers R, R and AvR "are audiorisignalsW-'hichjfare passed;on tothe primary :winding sofraudio. transformersr5,5 andf .5,' The .fsecon'dary Iwinding-of audio transformers 5, 5',

'5' .are.coupled.tothe cathodes of diodes .22,12 I2" whose anodes aredirectly connecteditogetherin .electricallyiparallel relation-by meansof.lead I'.

'A -portion fof ,the outputs. of the .intermediate .transformers f4,f.4.1iand -`f4' -to f rectiers l I and I, Whichvrectifytheintermediate Vfrequency vsignal. Rectier "I :is provided Withfa low'pass'.'flter 6 ,fi Ifand i9, .andia resistor l 8 from 'fwhch'ffdirectcurrentbiasfisavalableproportional '.tolthe `tion receiver employing alimiter.

individual signal strength in the output of its associated channel.Rectiers I and I" are each provided with similar low pass filters andassociated resistors having corresponding reference numerals with primedesignations. Low pass lter 6, 'I, 9 is designed to remove the amplitudemodulation component of the noise detected by diode I. It is essentialthat this noise be removed to prevent the amplitude modulation noisefrom appearing in output resistor I and thereby impairing thesignal-to-noise ratio of the signal from resistor I0. The direct currentbiases from the resistors across the rectiers I, I', I" are respectivelysupplied to one terminal of their associated audio transformers 5, or 5"and cause their associated diodes 2, 2' or 2" to draw current so thatthese diodes act as resistances which will pass the audio output signalfrom the receivers R, R', or R" through the transformers 5, 5' or 5". Anunbypassed output resistor I0 is provided in common to all three diodes2, 2', 2" so that if the bias fed to one of the diodes (for examplediode 2) is stronger than that fed to any of the other diodes 2' or 2",the voltage built up on resistor I0 will bias the other diodes 2' or 2receiving the weaker signals so that they (2', 2") will not draw currentand therefore will not pass the signals from transformers 5', 5". Itwill thus be seen that the diodes 2, 2' and 2" merely act as gates anddo not rectify.

The system of Fig. 1 is so designed that the weaker signals in thedifferent channels are switched off or prevented from contributing tothe useful output, whereas the stronger signal in any one channel ispermitted to contribute the entire useful output. A vacuum tubeamplifier 3 serves to amplify the audio signal and to supply theamplified audio signal to an audio transformer II whose Y:secondarywinding is shown connected to a suitable jack I3. Any desired acousticdevice, such as headphones or a loud speaker, yor for that matter anyaudio recording or repeating system can be connected to jack I3.

A group of rectifiers shown in box M and supplied with a common outputresistor (not shown) furnishes the AVC (automatic volume control)potential to the radio frequency amplifiers of the different channelsover the AVC lead. The inputs to the rectifiers in box M are connectedto the outputs of the different intermediate frequency amplifiers D, D',D" as shown in the drawing. It has been found that the system of Fig. 1is highly advantageous when the receiver R, R' or R" is a frequencymodulation or phase modula- Such an arrangement is described hereinafterin more detail in connection with Fig. 5. I have found that the maximumsensitivity of control is obtained in the system of Fig. 1 when thealternating current voltages at transformers 5, 5', 5 from the outputsof the receivers R, R', R" is relatively small. As an example, in oneexperimental ern- It should be noted that I have been able to separatethe direct current controlling bias from the voltages to be combined,and that I have provided an audio frequency output directly from thereceiver under control of the intermediate frequency rectified signal.The system of the invention thus allows a reduction in the level of thevoltages to be combined with a consequent limprovement in thesensitivity of the selecting action between the stronger and weakersignals. At this time I wish to point out that in the system of mycopending case now U. S. Patent 2,420,858 I provide a positivepolarizing potential over the common resistor in the outputs of thediodes Whereas no such polarizing potential is provided herein. This isbecause the system of the present invention requires less audiofrequency current passing through the transformers 5, 5 and 5" than ispresent in the outputs of the diodes in my U. S. Patent 2,420,868. Thissmaller magnitude of audio voltage in the present invention does' notallow a modulation of the current to a depth suicient to cause thenegative peak clipping which is produced by the higher audio voltages.

Fig. 2 is a modification of the system of Fig. 1 and illustrates amethod by which the intermediate frequency outputs of the differentchannels can be combined for utilization from a common output resistor I0'. In the circuit of Fig. 2, the transformers 4 supply energy to therectifiers I, I', I" and also combining diodes 2, 2', 2". Consideringchannel #t I, for example, the rectined signal from resistsor 8 is fedthrough low pass filter 6, 1, 9 and biases diode 2 through choke coil25. The intermediate frequency signal from transformer 4 is passedthrough condenser 24 and also appears on diode 2. The value of condenser24 is adjusted in order to feed the desired amount of intermediatefrequency to the diode 2. The choke coil 25 allows the intermediatefrequency energy passing through condenser 24 .to pass to rectifier 2and conducts the bias voltage from resistor 8 to diode 2. It will thusbe seen that I have been able (in Fig. 2) to separate the intermediatefrequency energy from the direct current bias and pass them overseparate paths (24 and 25) in order to superimpose them on one anotherat the diode 2 at a reduced level of intermediate frequency current. Iheoperation of the system of Fig. 2 is generally like that of Fig. 1,keeping in mind the foregoing modification.

In experiments tried out in connection with a system` like that shown inFig. 2, I have found that with about 0.085 R. M. S. volts fed fromcondenser 24 to the combining diodes 2, 2', 2", the control from onevchannel to another switched completely from one diode 2 to anotherdiode 2 or 2" with a change of merely 0.5 `volts plus or minus on one ofthe diode biases caused by a change in the intermediate frequencysignal. Hence, if the `rectified signal from resistor 8 were 10 volts,

the change in signal to effect the switch over from one channel toanotherwould be 5% or plus or minus 0.5 db. If therectied signal were 20volts (a likely value) the switch over from one channel to another wouldbe effected by a plus or minus 0.25 db. change in one radio frequencysignal with respect to the other one. 4

Fig. 3 shows one form of the invention useful for receiving phase orfrequency modulated signals. The circuit of this figure is highlydesirable for preventing a bucking or cancelling condition in theoutputs of the receivers normally brought about by an equality ofsignals of opposite phases phase deviation of the fundamental.-outputsfrom the differential diode circuits A3?, 34 and 31,38 are addedin series to-give a total audio output available for utilization in-audio emf intWo ormore channels. Ilhavernoticed .that for Lthe 180fout-of-phase 'condition for incoming signals, the wave-form-is that .of.-a second 'harmonic in the combinerfoutput. `By taking thesecondharmonic'from thecombiner output and adding it to the fundamentaloutput ina diversity receivingv combination, II-am able to'preven'tcancellation for the' signal buckingcondition. Fig.'3 showsonlyithatgportion of the sys'tenfrwhich apfrequency outputappearing'across the common .'15

kresistor Ifis 'fed over two paths. SI, .32, 33 and V34; and `35, 36,31and 38. One circuiti=3l,.3`2fis A-tunedto the fundamental frequencyiof.theintermediate frequency energy appearingracross r-esistorll', :whilethe othercircuit 35,136`is tuned tothe second kharmonic-of theyintermediate frequency energy and for twice vthe frequency or The Atwopliiier 3.

Fig. 4 shows another embodiment of theinvention'somewhat vsimilarto Fig.2, wherein. use is made of the so-ealled innite impedance electrondischarge devices 22, 22 and 22" (three element vacuum tube). This typeof iniiniteimpedance device has the advantage that its input does vnotdraw current, as a result-of which a resistance filter maybe used inplace of theinductyance type shownin Fig. 2, and a resistor i3 in Fig.f4 may 'replace thechoke coil 25 in Fig. 2. 'The 'mediate frequencyenergy, which may be either nfrequency, phaseor amplitude modulated; isysup'- plied to the transformers 4 and 4" inthe same manner as in Fig.2. An intermediate frequency output is available inthe common resistor Iwhich is connectedlbetween ground andthe cathodes of the infiniteimpedance diodes22, 22",

l22","as shown. The intermediate frequency'output across resistorIIl maybe'fe'd to either a frequency or phase or amplitude detector system,depending upon the type of modulated wave received by the system.

Fig. `shows Aa modification of the system of Fig. 1, particularlyadapted for combining the outputs of frequency modulation telegraphreceivers in the different channels. Generally stated, the transformers5, 5 and 5 in Fig. 1 'are vreplaced in Fig. 5fby differential dioderesistors incircuit with the-outputs of the frequency modulationreceivers. Fig. v5 provides a very simple meansof combining the detectedoutputs of the frequency modulation receivers in which separate limitersare inserted before the Ycombination. More specifically, Fig. 5comprises three channels'similar to Fig. 1, in which the receivers --R,R and-R arefrequency modulation receivers, each including a limiter L, Lor L, a frequency modulation discriminator F, or F" and, VA.

``6 and a `differential V.diode Yresistor fcircuitfN, N or N". Thedifferential. diode resistorsN .fN zand. N" each comprise a pair ofdiodes I6, .I6 whose anodes are coupled2to theoutputofthe. associatedfrequency modulation receiver xand'whose cathodes are connectedrtogether throughfequal :value resistors I1, as shown. These resistorsI1 are shunted byfsuitable by-pass condensers I8. This type ofdifferential diode resistor'fN, N ,or N is sometimes known as abalanceddiode circuit .and is Well known in theart, no claim being made toit'per se. Yllachcha'nnel is provided Witharectifier 50, '50?, 5I!"whichiis fed by the incoming frequency vinput to the signal through-.atransformer I 9 at the input of the limiter. The signal rectified by thediode 5I), 5B', and 5t :isfed .to the cathode of oneof the diodes I6, I6of the associated differentialdiode circuits in such-gmanvner that thediscriminator and `its differential diode circuit is floating at a biaspotential determined'by the rectifier 5E,15il'.,orV 5E". Automaticvolume control for the three channelsiroverfan AVC lead is obtained froma common fresistor (not shown) in circuit with the combined'zrecti- .nedoutputs of the radio frequency amplifiers supplied by apparatus 'M.inthe same manner asi-'in Fig. 1.

In the operation of the system .of Fig-5, letus assume that the signalto channel AI `is theastrongest of the signals received onthe antennasA,.A The rectified signal vfrom rectifier A50 will be fed to the diode'2 and will causediode'Z to act as a resistance and pass the :detectedsignals from the diierential diode circuit N. Y At the same time, thevoltage from rectier 5I) is in series with the diode l2 and appears -onVthe conductor output `resistor I0, `and'since this .signal is greaterthanthat obtained from either of the other rectiiiers 582. Eril", itWill lee-evident that the diodes 2 and are biased so that they do notdraw current and are therefore an open circuit insofar as the passage ofsignals from the differential 'diode' circuits N and N" are concerned.Hence, a selector action is effected whereby the 'strongest signal inone of the `three channels biases its respective output diode2, `2'

Vor 2" Ato operation and the remaining diodes to inoperation. The resultis a selection of the signal having the greatest amplitude at the inputof the limiter of the frequency modulation signal regardless of the factthat'the limiters hold the detected outputs of the three receiversat-the same amplitude.

An advantage of the system of Fig. 5'lies in the yelimination of the use`of controlled ampliers of the prior art and the complicated circuitsbrought about by their use.

It should be noted that the low-pass filters I5, 1 in Figs. 1 and '2,and the resistance filters 49 'in Figs. 4 and 5 are so designed thattheir cut-01T frequency is below the minimum modulation frequency vatthe receiver output. If thisis not done, the high signal-to-noise ratioobtained by the use of frequency modulation is impaired. This isespecially true if the frequency modulation output level is low comparedto the control voltage.

What is claimed is:

'1. In a diversity receiving system having a plurality of receiverchannels feeding a common utilization circuit, means for passing to saidutilization circuit the signal from only that receiver channel havingthe largest incoming voltage, said means including a rectifier and anelectron discharge device resistor in yeach receiver channel, andconnections for feeding both said rectifier and said electron dischargedevice resistor over separate paths with alternating current, and aconnection from the output of said rectifier to said electron dischargedevice resistor, whereby said rectifier serves to rectify thealternating current in said channel and said electron discharge deviceresistor passes the rectified current from said rectifier, and a commonload resistor for all of the discharge device resistors of saidchannels, whereby the passage of current through any one of saiddischarge device resistors produces a direct component of voltage dropin said load resistor which appears as a negative bias on the otherdischarge device resistors, as a .result of which the alternatingcurrent signal energy passed on to said utilization circuit iscontrolled by the rectified alternating current and the controlling biasis separated from the voltages to be combined.

. 2. In a diversity receiving system having a plurality of receiversfeeding a common utilization circuit, a rectifier in circuit with eachreceiver for rectifying the alternating current signal in each receiver,a tube for each receiver for passing the rectified current therefrom, aseparate path in each receiver for passing the alternating currentsignal to the same tube which passes the rectified alternating current,a common load resistor for said tubes connected thereto by a directcurrent connection, whereby the passage of current through any onetube'produces a component of voltage drop in said load resistor whichappears as a negative bias n the other tubes.

. .3. A diversity receiving system comprising a plurality of receivercharmels each of which includes a receiver for producing an audiofrequency signal, a rectifier coupled to each receiver for rectifyingthe alternating current signal of higher than audio frequency, a tubefor each channel in circuit with the output of the rectifier of thatchannel and adapted to pass the rectified current thereof, a commondirect'current imped ance element connected to the outputs of said tubesof all of said channels, and means aiso in circuit with the tube in eachchannel for supplying thereto the audio frequency signal, whereby therectified alternating current and the audio frequency signal flowthrough separate paths in each channel to said tube, and the audiofrequency signal passed by said tube is controlled by the rectifiedalternating current.

4. A diversity receiving system comprising a plurality of spacedantennas, individual superheterodyne receivers for said antenna-s, eachreceiver including an intermediate frequency amplifier and a rectifierfollowing said amplifier, said rectifier deriving energy from the outputof said intermediate frequency amplifier, a tube coupled to the outputof the rectifier of each receiver, a common direct current impedancecoupled to the outputs of said tubes, whereby the flow of currentthrough any one of said tubes `causes a direct current to flow throughsaid common impedance and produces a negative bias ori the other tubesin circuit with the other receivers, and an alternating currentconnection between the output of the intermediate frequency amplifier ineach receiver and said tube in circuit with the same receiver.

5. A diversity receiving system comprising a plurality ofsuperheterodyne receiver channels each of which includes a rectifier forrectifying the alternating current signal output thereof, diodesrespectively in circuit with the rectiers including a cathode connecteddirectly to ground,

a low pass filter shunted by a resistor in the space current path ofsaid rectifier, said filter being located between the cathode andanother electrode of said rectifier, a diode for the output of eachrectifier and having a cathode coupled over a path capable of passingdirect current to that terminal of said resistor which is farthest awayfrom the cathode of said rectifier, means for directly connectingtogether the anodes of the diodes associated with the different receiverchannels, a common load resistor having one terminal directly connectedto the anodes of said diodes and another terminal connected to ground,and a path for supplying the diode in each channel with unrectiiiedintermediate lfrequency energy in said same channel.

7. A receiving system for angular velocity waves, comprising in theorder named a radio frequency amplifier, a frequency converter, anintermediate frequency amplifier, a limiter coupled to the output ofsaid last amplifier, a discriminator following said limiter, and adifierential type detector for rectifying the output of saiddiscriminator, said differential type detector including a pair of tubeshaving theircathodes connected together, an electron discharge devicetype of resistor coupled to the output of said differential typedetector, a load resistor connected to the output of said electrondischarge device resistor, a rectifier coupled to the output of saidintermediate frequency amplifier, a direct current connection betweenthe output of said rectifier and the cathode of one tube of saiddifferential type detector for biasing said Vdetector at a biaspotential determined by said rectifier, and a utilization circuitcoupled to said load resistor.

8. A receiving system for angular Velocity waves, comprising in theorder named a radio frequency amplifier, a frequency converter, anintermediate frequency amplifier, a limiter coupled to the output ofsaid last amplifier, a discriminator following said limiter, and adifferential type detector for rectifying the output of saiddiscriminator, said differential type detector including a pair of'tubeshaving their cathodes connected together, a diode having its cathodeconnected through a connection capable of passing direct current to thecathode of one tube of said differential type detector, a load resistorhaving one terminal connected to the anode of said diode and its otherterminal connected to a point of fixed radio frequency potential, and arectifier coupled to the output of said intermediate frequency amplifierand having its output coupled to the cathode of the other tube of saiddetector for supplying the cathode of the other tube of said detectorwith a bias potential determined by the magnitude of signal rectified bysaid rectifier.

9. A diversity system in accordance with claim 2', including a pair ofsignal paths having their inputs coupled in parallel relation andconnected to said common load resistor, one of said signal pathsincluding a limiter and a discriminator both tuned to the fundamental ofthe intermediate frequency energy appearing across said common loadresistor, the other of said signal pathsincluding a limiter and adiscriminator both tuned to the second harmonic of the intermediatefrequency energy and being adjusted for twice the frequency or phasedeviation of said fundamental, and a connection adding in series theoutputs from said discriminators.

10. In a diversity receiving system for receiving frequency modulatedwaves, a plurality of receiving channels feeding a common utilizationcircuit, each of said channels including a radio frequency amplifier, afrequency converter, an intermediate frequency amplifier, a limiterfollowing said intermediate frequency amplifier, a frequency modulationdiscriminator in the output of said limiter, a differential diodecircuit in the output of said discriminator, and a vacuum tube resistorcoupled to said differential diode circuit, a rectifier coupled betweenthe output of said intermediate frequency amplifier and saiddifferential diode circuit for rectifying the intermediate frequencysignal and for applying the resultant rectified voltage as a directcurrent bias to said diode circuit, whereby said discriminator andassociated differential diode circuit operates at a varying bias voltagedetermined by the magnitude of the rectified intermediate frequencysignal, a connection coupling the outputs of said vacuum tube resistorsin electrically parallel relation, and a common load resistor .connectedto said connection, whereby the passage of current through said commonload resistor due to the flow of rectified current in one channelproduces a negative bias on the other vacuum tube resistors.

11. In a diversity receiving system for receiving frequency or phasemodulated waves, a plurality of receiving channels, coupled to differentenergy pick-ups each `channel feeding a common utilization circuit, eachof said channels including a radio frequency amplifier, a frequencyconverter, an intermediate frequency amplifier, and a frequency or phasemodulation detector following said last amplifier, a vacuum tuberesistor coupled to the output of said detector, a rectifier coupled tothe output of said intermediate frequency amplifier and having itsoutput coupled to said vacuum tube resistor for rectifying theintermediate frequency signal and for applying the resultant rectifiedvoltage on the detected intermediate frequency signal voltage suppliedby said detector to said vacuum tube resistor, a low pass filter in saidrectifier, connections coupling the outputs of said vacuum tuberesistors in said plurality of channels in electrically parallelrelation for direct current, and a common load resistor for the outputsof said vacuum tube resistors.

12. In a diversity receiving system having a plurality of receiverchannels feeding a common utilization circuit, means for passing to saidutilization circuit the signal from only that receiver 10 channel havingthe largest incoming voltage. said means including a first rectifier ineach receiver channel for rectifying the alternating current in thatchannel, and also including an electron discharge device resistor forpassing the rectified current from the first rectifier, and anunbypassed common load resistor for al1 of the discharge deviceresistors of said channels, whereby the passage of current through anyone of said discharge device resistors produces a direct component ofvoltage drop in said load resistor which appears as a negative bias onthe other discharge device resistors, and a path in each receiverchannel for supplying its associated discharge device resistor withalternating current signal Y energy, as a result of which thealternating current signal energy passed on to said utilization circuitis controlled by the rectified alternating current.

13. A diversity receiving system comprising a plurality of spacedantennas, individual superheterodyne receivers for said antennas, eachreceiver including an intermediate frequency am plifier and a rectifierfollowing said amplifien;

said rectifier deriving energy from the output of said intermediatefrequency amplifier, a tube coupled to the output of the rectifier ofeach receiver, a common direct current impedance coupled to the outputsof said tubes, whereby the fiow of current through any one of` saidtubes causes a direct current to flow through said common impedance andproduces a negative bias on the other tubes in circuit with the otherreceivers, and a path in circuit with each receiver for supplying thesaid tube associated therewith with alternating current signal energywhich bypasses the rectifier for that receiver.

14. A diversity receiving system as dened in claim 6, including a pairof signal paths having their inputs coupled in parallel relation and.connected to said common load resistor, one of said signal pathsincluding a limiter and a discriminator both tuned to the fundamental ofthe interi mediate frequency energy appearing across said common loadresistor, the other of said signal paths including a limiter and adiscriminator both tuned to the second harmonic of the intermediatefrequency energy and being adjusted for twice the frequency or phasedeviation of said fundamental, and a connection adding in series theoutputs from said discriminators.

' MURRAY G. CROSBY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

